Department of Applied Physics, Nagoya University, Furo-cho, Nagoya 464-8603, Japan.
Department of Physics, Nagoya University, Furo-cho, Nagoya 464-8602, Japan.
Phys Rev Lett. 2014 May 9;112(18):187001. doi: 10.1103/PhysRevLett.112.187001. Epub 2014 May 6.
The isostructural transition in the tetragonal phase with a sizable change in the anion height, is realized in heavily H-doped LaFeAsO and (La,P) codoped CaFe2As2. In these compounds, the superconductivity with higher Tc (40-50 K) is realized near the isostructural transition. To find the origin of the anion-height instability and the role in realizing the higher-Tc state, we develop the orbital-spin fluctuation theory by including the vertex correction. We analyze LaFeAsO(1-x)H(x) and find that the non-nematic orbital fluctuations, which induce the anion-height instability, are automatically obtained at x∼0.5, in addition to the conventional nematic orbital fluctuations at x∼0. The non-nematic orbital order triggers the isostructural transition, and its fluctuation would be a key ingredient to realize higher-Tc superconductivity of order 50 K.
在高度掺杂的 LaFeAsO 和 (La,P) 共掺杂的 CaFe2As2 中，实现了四方相结构中阴离子高度发生显著变化的同构转变。在这些化合物中，超导转变温度 Tc 更高（40-50 K），接近同构转变。为了找到阴离子高度不稳定性的起源及其在实现更高 Tc 态中的作用，我们通过包含顶点修正发展了轨道-自旋涨落理论。我们分析了 LaFeAsO(1-x)H(x)，发现除了在 x∼0.5 时存在常规的向列轨道涨落之外，还自动获得了诱导阴离子高度不稳定性的非向列轨道涨落。非向列轨道有序触发了同构转变，其涨落可能是实现高达 50 K 的超导性的关键成分。
